This invention relates to a device for tensioning elongated elements such as wire ropes, chains, bolts, rods or the like. In particular it is intended for use in the construction or mining industry for tensioning mechanical anchors, reinforcing rods and so on which are used to stabilize and support the walls of rock or ground excavations.
Mechanical rock anchors, concrete reinforcing cables and the like are typically tensioned, once anchored, by means of a removable hydraulic cylinder jack which is heavy and cumbersome to operate and manoeuvre in underground workings and particularly in the confined work space in many mine workings.
A tensioning device according to the invention comprises an inflatable pressure vessel having two superimposed major wall components characterised in that the vessel includes an aperture which passes through both major wall components and a valve for filling the vessel with liquid under pressure to cause the vessel to be inflated in the axial direction of the aperture. The pressure vessel is conveniently made from sheet metal.
The major wall components may be sealingly connected about their outer peripheries and on the periphery of the aperture. The pressure vessel and its aperture are preferably circular about the axis of the aperture.
The tensioning device may include a bellows arrangement which is connected to and located between the two major wall components of the pressure vessel around the aperture. The device may additionally include a second bellows arrangement which is connected to and located between the outer peripheries of the two major wall components of the pressure vessel.
In another form of the invention the pressure vessel includes an upstanding peripheral wall and one of the major wall components of the vessel is inwardly dished from the upper end of the wall towards the outer major wall component. Conveniently the upper end of the wall of the vessel is substantially rounded.
In certain applications the tensioning device may include a pressure indicating device which is open to the cavity of the pressure vessel.
A method of tensioning an elongated member such as a metal rod, rope or the like by means of the above tensioning device characterised in that according to the invention the method includes the steps of anchoring the elongated member in a body, passing one end of the member through the aperture of the tensioning device on the outside of the body of material, bringing a first major wall component of the device to bear on a surface of the body, locating a pressure plate over the elongated member and against the second major wall component of the tensioning device, locking the pressure plate against the tensioning device by means engaged with the elongated member and inflating the tensioning device pressure vessel by means of liquid under pressure to cause its two major wall components to move away from each other to tension the elongated member between its anchor in the body and the pressure plate.